using System.Collections.ObjectModel;
using FluentResults;
using Npgsql;

namespace pgLabII.PgUtils.ConnectionStrings;

/// <summary>
/// Parser for converting a libpq style connection string into a dictionary of key value pairs
/// </summary>
public ref struct PqConnectionStringParser
{
    // Note possible keywords
    // host
    //hostaddr 
    //port
    //dbname
    //user
    //password
    //passfile
    //channel_binding
    //connect_timeout
    //client_encoding
    //options
    //application_name
    //fallback_application_name
    //keepalives
    //keepalives_idle
    //keepalives_interval
    //keepalives_count
    //tcp_user_timeout
    //replication
    //gssencmode
    //sslmode
    //requiresll
    //sslcompression
    //sslcert
    //sslkey
    //sslpassword
    //sslrootcert
    //sslcrl
    //sslcrldir
    //sslsni
    //requirepeer
    //ssl_min_protocol_version
    //ssl_max_protocol_version
    //krbsrvname
    //gsslib
    //service
    //target_session_attrs

    public static Result<IDictionary<string, string>> Parse(string input)
    {
        return new PqConnectionStringParser(
            new PqConnectionStringTokenizer(input)
            ).Parse();
    }

    private readonly IPqConnectionStringTokenizer _tokenizer;
    private readonly Dictionary<string, string> _result = new();

    public PqConnectionStringParser(IPqConnectionStringTokenizer tokenizer)
    {
        this._tokenizer = tokenizer;
    }

    public Result<IDictionary<string, string>> Parse()
    {
        _result.Clear();

        while (!_tokenizer.IsEof)
        {
            var result = ParsePair();
            if (result.IsFailed)
                return result;
        }

        return _result;
    }

    private Result ParsePair()
    {
        var kwResult = _tokenizer.GetKeyword();
        if (kwResult.IsFailed)
            return kwResult.ToResult();
        var result = _tokenizer.ConsumeEquals();
        if (result.IsFailed)
            return result;
        var valResult = _tokenizer.GetValue();
        if (valResult.IsFailed)
            return valResult.ToResult();
        
        _result.Add(kwResult.Value, valResult.Value);
        return Result.Ok();
    }

    private SslMode ToSslMode(ReadOnlySpan<char> v)
        => v switch
        {
            "disable" => SslMode.Disable,
            "allow" => SslMode.Allow,
            "prefer" => SslMode.Prefer,
            "require" => SslMode.Require,
            "verify-ca" => SslMode.VerifyCA,
            "verify-full" => SslMode.VerifyFull,
            _ => throw new ArgumentException("Not a valid SSL mode"),
        };

}